In the field of electronic system manufacturing, the use of surface mount technology to attach and connect integrated circuit components onto printed circuit boards has continued to grow. As is known in the art, surface mountable integrated circuit packages have leads which are folded or bent to allow for their solder connection to a planar surface of a circuit board, eliminating the need for plated-through holes through the circuit board. Surface mount technology thus increases the theoretical component density of the circuit board, as well as the degrees of freedom available to the board designer, as the location of integrated circuit leads need only be considered for a single surface plane of a multi-layer circuit board, rather than for all planes of the board.
However, the surface mountable integrated circuit is subjected to greater thermal and mechanical stress during the assembly procedure than are integrated circuits of the dual-in-line and similar package types. The mounting of a dual-in-line integrated circuit package to the circuit board is accomplished by wave solder of the underside of the circuit board (i.e., the side opposite that of the integrated circuit), as the pins of the integrated circuit package extend through plated-through holes in the circuit board. Accordingly, the circuit board itself insulates the integrated circuit package body from the high solder temperatures and harsh chemicals to which the soldered lead tips are subjected. Since the leads of a surface mountable package are soldered at the same surface at which the integrated circuit package body is located, however, the integrated circuit package body and its contents are directly subjected to the high temperature of the flowing solder, and to harsh chemicals used in the soldering process, such as flux, solder, and cleaning solvents.
Conventional surface-mountable integrated circuits that contain only a semiconductor device and its wire connections are generally able to withstand the thermal, chemical and mechanical stresses presented by the surface mount process. As such, the use of surface mount techniques in the manufacture of circuit boards of many types has become widespread, obtaining the density advantages provided by this technology.
In recent years, the use of battery power for many electronic circuit functions has become available, primarily due to advances made in complementary metal-oxide-semiconductor (CMOS) fabrication and design technology. As is well known, CMOS integrated circuits are able to operate with extremely low active power requirements; in the case of CMOS memory devices, such as static random access memories (SRAMs), the power requirements for data retention are especially low. These low power requirements allow operation and data retention in electronic systems to be powered by conventional lithium batteries and other cell types, improving the portability and reliability of modern electronic systems.
It has therefore become desirable to provide a battery with an integrated circuit in a single package, so that battery backup functionality may be easily implemented in the system. Copending U.S. patent application Ser. No. 07/995,665, filed Dec. 21, 1992 and entitled "Surface Mountable Integrated Circuit Package with Integrated Battery Mount", assigned to SGS-Thomson Microelectronics, Inc. and incorporated herein by this reference, describes an example of packages containing both a semiconductor integrated circuit and a battery, for use in surface mount applications.
As described in this application, conventional batteries are unable to reliably withstand the temperatures and chemical conditions to which an integrated circuit is subjected during surface mount assembly, however. For example, some types of batteries can be irreparably damaged by exposure to temperatures as low as 181.degree. C., which is below the temperature of certain solders used in the surface mount process. Other components, such as quartz crystal resonators used in connection with on-chip oscillators, are also vulnerable to these harsh environmental conditions. The harsh chemical environment of the surface mount process can also damage the physical construction of these components.
By way of further background, copending U.S. patent application Ser. No. 08/105,301, filed Aug. 11, 1993 and entitled "Molded Package Integrated Circuit with Electrochemical Cell", assigned to SGS-Thomson Microelectronics, Inc. and incorporated herein by this reference, describes an example of a molded integrated circuit package having a battery molded therein.
It is therefore an object of this invention to provide a surface mountable integrated circuit package adapted to receive a module containing temperature-sensitive components, where the module can be readily attached after surface mount of the integrated circuit package.
It is a further object of the present invention to provide such a package where the module is removable for replacement during system life.
It is a further object of the present invention to provide such a package where the module contains a battery.
It is a further object of the present invention to provide such a package where the module can only be assembled in one orientation to prevent misassembly.
It is a further object of the present invention to provide an integrated circuit package with battery-power in which the battery may be replaced for environmentally-sound disposal.
By way of further background, certain system applications install circuit boards with close spacing relative to one another. As a result, the height of components when installed on the circuit board must be kept very low. Despite the height limitations, these circuit boards still require efficient use of their surface area, so that the "footprint" of the integrated circuit packages mounted thereon must also be minimized.
It is therefore a further object of the present invention to provide surface mountable integrated circuit package adapted to receive a module containing temperature-sensitive components, where the module can be readily attached after surface mount of the integrated circuit package, and in which the height of the package with module is minimized.
It is a further object of the present invention to provide such an integrated circuit package which does not have an increased footprint while still reducing the package and module height.
Other objects and advantages will be apparent to those of ordinary skill in the art having reference to this specification in combination with the drawings.